This work by Aquinas begins by discussing different types of political systems, using the classical classifications. Only rule which is directed "towards the common good of the multitude is fit to be called kingship," he argues. Rule by one man who "seeks his own benefit from his rule and not the good of the multitude subject to him" is called a "tyrant." He argues that "Just as the government of a king is the best, so the government of a tyrant is the worst," maintaining that rule by a single individual is the most efficient for accomplishing either good or evil purposes. He then proceeds to discuss "how provision might be made that the king may not fall into tyranny," stressing education and noting that "government of the kingdom must be so arranged that opportunity to tyrannize is removed." He then proceeds to consider what honor is due to kings, to discuss the appropriate qualities of a king, and to make some points on founding and maintaining a city.

Principium autem intentionis nostrae hinc sumere oportet, ut quid nomine regis intelligendum sit, exponatur.